Marfan syndrome (MPS) is a common connective tissue disorder caused by mutations In flbrillln-1, the major Structural component of extracellular microfibrils. We originally speculated and have subsequently demonstrated that flbrlllln-1 mutations Impair the sequestration of latent TGFB complexes In the extracellular matrix (ECM) with deleterious consequences to cellular performance. This seminal discovery has led to the realization that TGFB blockade (specifically through losartan-mediated antagonism of angiotensin II receptor I activity) is a productive strategy to mitigate systemic manifestations in mouse models of MFS and human patients. Our work has also identified additional disease-causing processes that represent potential new targets for treatment of MFS and that are the focus of this renewal application. The disease-causing processes that will be investigated in the next funding cycle Include developmentally-lmposed changes of endothelial cell fate secondary to promiscuous TGFB signaling (Project 1), cellular and extracellular events leading to constitutive TGFB activation (Project 2), matrix-Induced perturbations of aorta homeostasis and repair (Project 3), and improper p38 MAPK activity and unbalanced TGFB and BMP signaling in the vascular and skeletal systems, respectively (Project 4). These different aspects of MFS pathogenesis will be interrogated in mouse models of the disease that are also deficient In relevant signaling molecules or that are treated with Inhibitors of specific effectors. Mouse-based analyses will be complemented and expanded by in vitro studies of mutant cells and tissues. As In the past, the highly Integrated effort of our research program is based on the unique but overlapping hypotheses of the four projects, whose ultimate amalgamation will delineate how initial ECM alterations are translated into aberrant cellular responses in MFS. Furthermore, the specialized services of the Administrative Core (Core A) and the Imaging and Antibodies Core (Core B) will continue to provide critical support to the research activities of our Consortium. RELEVANCE: MFS represents a unique example of a monogenic disorder that has informed our understanding of tissue degeneration and our ability to mitigate disease progression using a drug-based therapy. The proposed studies will further advance this knowledge by identifying new biological targets for therapy, as well as prognostic biomarkers of vascular and skeletal manifestations, which constitute the major mortality and morbidity factors in MFS.